1. Field of the Invention
The invention relates to a method for producing a bent pipe from thermoplastic material.
2. Description of the Background Art
The bending of straight lengths of pipe into bent pipes by means of press bending, roll bending or 3-roller bending is known in mechanical engineering. In the production of bent pipes for pipe networks, the prime objective is to achieve high production precision. High production precision takes the form of maintaining narrow positional tolerances of end regions of pipes that can be installed at their intended location without additional bending stress. In particular in the case of pipe networks, in which stress-free installation must be ensured for technical reasons, production with high accuracy is absolutely necessary. Production precision in the case of bent pipes also takes the form of maintaining the roundness of the bent pipe. Deviations from the circular cross-section of a pipe, known as ovality, in the end cross-section make it more difficult to make a connection to another pipe to which the bent pipe is intended to be connected. Furthermore, ovality between end cross-sections of a pipe in which fluid is carried under varying pressure has the effect that the region with the oval cross-section has a short lifetime. Furthermore, many technical areas in which bent pipes are used strive for weight-saving constructions, and aim to use plastic pipes instead of metal pipes.
GB 2 390 566 A discloses a method for bending a thermoplastic pipe in which a thermoplastic pipe is bent in a heated state around a bending body. An infrared emitter is used there for heating the thermoplastic pipe. Furthermore, in a final step, the heated bent pipe is cooled. A disadvantage of this method is the high thermal distortion and the limited production precision.